Solve the Differential Equation $$25 y ^ { tt } + y = 0$$

Solve the differential equation. Select the correct answer.
$$25 y ^ { tt } + y = 0$$

A)
$y ( x ) = c _ { 1 } \cos \left( - \frac { x } { 25 } \right) + c _ { 2 } \sin \left( - \frac { x } { 5 } \right)$
B) $y ( x ) = c _ { 1 } \cos ( - 5 x ) + c _ { 2 } \sin ( - 5 x )$
C) $y ( x ) = c _ { 1 } \cos \left( \frac { x } { 5 } \right) + c _ { 2 } \sin \left( \frac { x } { 5 } \right)$
D) $y ( x ) = c _ { 1 } \cos ( 25 x ) - c _ { 2 } \sin ( 25 x )$
E) $y ( x ) = c _ { 1 } \cos ( 5 x ) + c _ { 2 } \sin ( 5 x )$